As wireless communication services become more popular, the need for providing wireless communication services where those desiring such services may be located also increases. Moreover, such wireless service demand increases introduce problems in providing enough capacity in areas where such wireless communication services are provided.
In order to provide for free roaming wireless telephone communications wireless cellular telephone networks have been deployed throughout many populated areas. Such systems rely on the use of predefined areas of channel reuse in order to utilize a limited amount of radio frequency spectrum in serving a particular capacity of wireless communications. Accordingly, radiation of a particular communication channel is limited to within a particular area associated with a cellular base transceiver station (BTS).
Such systems generally suffer from coverage gaps or holes where a particular BTS is unable to radiate a signal or channel with attributes suitable for use in conducting communications over the network due to such obstructions as large buildings. Often it is difficult or impossible to sufficiently fill in these gaps with signals radiated from adjacent BTSs of the cellular network because of resulting problems with overlapping radiation patterns in areas unaffected by the obstruction, multiple obstructions such as buildings in a metropolitan area blocking signals from multiple adjacent BTSs, and the like.
Moreover, often the areas associated with such gaps in communication service coverage are areas of more dense congregation of those desiring such wireless services. For example, large numbers of persons desiring to use wireless mobile subscriber units (MSU) may be present within urban buildings which are shaded from signals radiated from BTSs of a communication network by the structure of the building itself or other buildings located in the communication path.
Similarly, although within an area providing suitable communication with a BTS of a cell encompassing such a building, the concentration of persons desiring wireless communication services may demand capacity not available from such a cell. Accordingly, enhanced capacity may be provided by disposing a cell, or microcell, to service such a concentration, i.e., a cell disposed to service communications associated with MSUs located within or near a high rise office tower.
Accordingly, solutions have been offered which deploy antennas, coupled to a transceiver of a communication network, within buildings in order to provide wireless communication services therein. However, such prior art solutions have often been limited to combining the signals of all or a plurality of the antennas disposed in the building and providing the combined signals to the transceivers. Such an approach suffers from disadvantages such as the signal provided to each transceiver includes the noise initially present on only one or a few antennas, such as a particular interfering signal from outside the building, because the antenna signals are combined. Moreover, the sum of such noise being present on multiple ones of the antennas can result in the noise exceeding limits for an acceptable carrier to interference (C/I) ratio. Accordingly, the number of such antennas is generally limited to a small number in order to maintain a desired signal quality level. Additionally, due to the signal loss issues associated with the antenna feed network of these prior art systems, the deployment of these prior art antennas is limited to relatively short distances from the associated transceiver.
In order to overcome some of the above described problems, other prior art systems have utilized transceivers distributed throughout the communication coverage area, i.e., deployed throughout a building in which communication is to be provided. However, such a solution presents substantial disadvantages also. Specifically, by definition such a solution requires multiple, and often expensive, transceivers to be deployed in order to provide communications in more than one area of the building. Moreover, the deployment of multiple transceivers capable of communicating on a same channel in order to provide this channel within multiple portions or an increased portion of the area serviced involves the inefficient use of such transceivers and/or channels. Furthermore, the use of such transceivers does not readily provide capacity for multiple simultaneous communications within a particular area without deploying multiple ones of the transceivers to provide communications within each such area, thus further aggravating inefficiencies associated with the deployment of transceivers throughout the service area. Additionally, the distributed deployment of transceivers substantially complicates the control mechanism required to operate such a communication network in addition to requiring added communication paths including control signal paths for each transceiver.
Accordingly, a need exists in the art for a wireless communication system adapted to provide communication within a limited area of service, such as within a building, wherein antenna signals are maintained distinct while providing efficient use of transceiver equipment, including allowing for the use of an assigned channel to xe2x80x9cfollowxe2x80x9d the movement of a unit in communication with a particular transceiver as the unit moves from the coverage area of one antenna to that of another and/or providing dynamic capacity availability to address capacity demand changes within the area of service. A further need exists in the art for such a system to be adapted to utilize a number of antennas sufficient to provide a desired cumulative area of coverage even where physical barriers, such as floors or walls of the aforementioned building, prevent each individual antenna from providing coverage within a substantial portion of the total area to be covered.
Additionally, a need exists in the art for the wireless communication system to be adapted to require a minimum of signal paths as between the antennas and transceiver equipment in order to provide the desired communications. A still further need exists in the art for such signal paths to allow for the disposal of antennas a substantial distance from transceiver equipment coupled thereto.
These and other objects, features and technical advantages are achieved by a system and method which utilizes a plurality of antennas strategically deployed throughout an area to be provided wireless communication service and coupling such antennas to transceiver equipment, i.e., radios, of a BTS or BTSs such that a particular antenna may be selected for communication of a particular transceiver signal. Accordingly, the transceivers of the BTS may be centrally located and thus easily centrally controlled and/or coupled to additional components of the communication network such as a public switched network (PSN) or mobile switching office (MSO). Moreover, as transceivers of the BTS may selectively communicate via ones of the plurality of antennas, efficient use may be made of such transceivers. For example, a single transceiver may be deployed for each channel of a plurality of channels utilized by such a communication system and yet communications may be established and maintained on a particular channel throughout all or a substantial portion of the coverage area utilizing only a single transceiver associated with this particular channel.
The preferred embodiment of the present invention utilizes switched beam or smart antenna technology in order to provide a plurality of antenna beams throughout the area to be covered which may then be selectively utilized by ones of the BTS radios. Accordingly, directional, either fixed beam or adaptive array, antennas are placed throughout the area to be covered, such as by deploying multiple antennas on each floor of a building and directing their antenna beams to illuminate substantially only areas within the building. As MSUs, or other wireless communication units including fixed subscriber units (FSUs), initiate or accept communications, a particular antenna having a radiation pattern encompassing the subscriber unit may be selected for use in servicing the communication. A controller operating according to the present invention may then provide the signal of this antenna to a proper BTS transceiver, i.e., a transceiver adjusted to communicate via a channel corresponding to that of the MSU, in order that a communication link is established/maintained. Preferably, as the MSU moves within the coverage area of the BTS or other events occur which affect the wireless link between the aforementioned antenna and MSU, such that another antenna of the plurality coupled to the BTS provides a more suitable wireless link with the MSU, the controller operates to provide the signal of this second antenna to the proper BTS transceiver. Accordingly efficient use may be made of each BTS transceiver as the transceivers may be utilized for servicing communications throughout substantial portions, if not all, of the area serviced by the BTS. Moreover, as only selected antenna signals are provided to such transceivers, the quality of such communications may be maintained with reduced amounts of noise as compared to prior art systems.
It should be appreciated that the antennas of the preferred embodiment described above may be utilized to service more than a single MSU. For example, where multiple MSUs are located within an area encompassed by the radiation pattern of one antenna of the present invention, the controller may provide the signal of this antenna to multiple BTS transceivers, i.e., a transceiver adjusted to communicate via a first channel (whether a frequency division channel, time division channel, code division channel, or otherwise) corresponding to that of the first MSU and a transceiver adjusted to communicate via a second channel (also whether a frequency division channel, time division channel, code division channel, or otherwise) corresponding to that of the second MSU. Likewise, where MSUs in communication with a same transceiver of the BTS are located within areas encompassed by the radiation patterns of different antennas of the present invention, the controller may provide the signal of each of these antennas to a single BTS transceiver, i.e., a transceiver utilizing different time division channels of a frequency associated with this transceiver to communicate with multiple MSUs may be coupled to multiple ones of the antennas either persistently throughout the communications with these units or in synchronization with the use of the appropriate channel. Accordingly, the present invention efficiently provides increased communication capacity throughout all portions of the service area.
A preferred embodiment of the present invention deploys at least a portion of the antennas utilized along the outer periphery of the service area, such as at the corners of each floor within a building to be provided with communication services. Accordingly, the communicated signals will be directed within the service area providing less interference to wireless systems outside the service area as well as accepting less interference from outside the service area.
Moreover, as users of MSUs operating therein may generally expect such communication services to be provided from sources external to the actual service area, i.e., cellular towers disposed external to a building within which they are operating, these users may be prone to migrating toward the periphery of the service area in an effort to achieve improved signal quality. Deployment of antennas along such periphery allows MSU transmission powers to be reduced as the MSUs migrate toward the periphery of the service area. Accordingly, when operating in areas most likely to result in transmitted signals being sufficient to interfere with wireless systems outside the service area, the transmission levels of a preferred embodiment are reduced to mitigate such interference. Moreover, as these MSUs are by definition closing the air gap between the MSU and a communication system antenna by migrating to the periphery of the service area, the system signal strength as received by the MSU may be improved with respect to an interfering signal associated with wireless systems outside the coverage.
According to one embodiment of the present invention, preamplifiers are disposed in the BTS receive signal path at a point near ones of the antennas. Therefore received signals may be amplified for transmission over a somewhat lengthy or otherwise lossy cable. Accordingly, antennas of this preferred embodiment may be disposed relatively large distances from the associated transceiver equipment. As such, wireless communications may be provided in areas located significant distances from the transceiver, such as in the upper floors of a high rise office tower, while allowing centralized deployment and control over a plurality of transceivers, such as may be deployed in a basement mechanical closet of the high rise office tower. Additionally, or alternatively, use may be made of lossier cable, i.e., less expensive cable, interconnecting the antennas and transceivers or transmission cable which is already available within the area to be served with wireless communications, i.e., computer systems networking cable deployed within a structure.
Additionally or alternatively, a preferred embodiment of the present invention utilizes frequency conversion in the signal paths near the antennas to convert received/transmitted signals to/from system native radio frequencies (RF) and intermediate frequencies (IF). Likewise, frequency conversion is utilized in the signal paths near the transceivers to convert the received/transmitted signals to/from RF and IF. Accordingly, by using a different IF for the RF signal received at ones of the antennas, some or all the antenna signals may be multiplexed onto a single signal path, i.e., a single coax. Moreover, by proper selection of the IFs used, ones of the antenna signals may be combined on an existing signal path which is also utilized by another communication service, such as the aforementioned computer systems networking cable.
According to this embodiment of the present invention, antenna selection for each transceiver may be accomplished by selecting a local oscillator (LO) frequency which up converts only that IF corresponding to the antenna selected to the exact carrier frequency that the transceiver serving a particular MSU is tuned for. This operation may be performed for multiple antenna beams with respect to a single transceiver, such as on a time slot by time slot basis for time division multiple access systems (TDMA) as TDMA MSUs may be dispersed throughout the coverage area yet each is served by the best antenna. Multiple antennas may be placed in communication with a single transceiver, to provide the multiple access techniques described above or for other purposes such as to provide signal diversity, by tuning the LO of multiple antennas to a common frequency.
With respect to the transceiver transmit signals, each transceiver may have a particular IF associated therewith such that multiple signals are combined for communication through a single cable. Accordingly, a particular antenna or antennas may be selected for transmission of a transceiver signal by selecting a LO frequency which up converts only that IF corresponding to this particular transceiver in order to radiate the transceiver""s signal within a desired portion of the coverage area. If more than one carrier is to be transmitted from a single antenna or combination of antennas, the LOs associated with these transceivers may down convert these carriers within the same IF band, thus allowing selection of a corresponding LO at the antenna for up conversion of all of these carrier frequencies.
Of course, there is no limitation to the use of a common signal path, i.e., the use of IFs for the combining of signals on a single cable, in both the transmit and receive signal paths. For example, a common cable may be utilized in the receive signal path and individual cables utilized in the transmit signal path, if desired.
The use of IFs as in the above described preferred embodiment provides advantages where substantial distances are present between antennas and transceivers. As lower cost transmission cable may often be utilized in providing a signal path for lower frequency communications, down conversion of the system native RF frequencies to a lower IF frequency is utilized by a preferred embodiment of the present invention in order to provide for cost effective communication of such signals over distances such as those of the above described high rise office tower. An alternative embodiment of the present invention utilizes conversion between the system native RF and lightwave signals for transmission through low-loss fiber.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.